The present invention relates to a printing method for forming an image on a substrate by means of a printer including a plurality of ink-filled chambers, each of which containing a nozzle operatively connected to a piezoelectric actuator, the method including the image-wise energization of the actuators to generate a pressure wave in each of the chambers so that ink drops are ejected from the nozzles of the chambers, and measuring the pressure wave in the chamber using a piezoelectric actuator operatively connected to said chamber. The present invention also relates to a printer adapted to this method.
A method of the above kind is known from European application EP 1 013 453. The inkjet printer of the piezo electric type known from this application has a printhead containing a number of ink chambers (also termed “ink duct” or, in short, “duct”), each chamber being operatively connected to a piezoelectric actuator. In one embodiment, an ink chamber has a flexible wall which is deformable by energization of the actuator connected to said wall. Deformation of the wall results in a pressure wave in the chamber and given sufficient strength this will result in the ejection of an ink drop from the nozzle of the chamber. The pressure wave in turn, however, results in deformation of the wall, and this may be transmitted to the piezoelectric actuator. Under the influence of its deformation the actuator will generate an electrical signal. This signal is directly dependent on the generated pressure wave in the chamber. Thus by measuring this signal the pressure wave in the associated chamber is measured indirectly.
From the said application it is known that analysis of this signal enables information to be obtained concerning the state of the ink chamber corresponding to said actuator. Thus it is possible to derive from this signal whether there is an air bubble or other irregularity in the chamber, whether the nozzle is clean, whether there are any mechanical defects in the ink chamber, and so on. In principle, any irregularity influencing the pressure wave itself can be traced by analysis of said signal. By using this known method, it is also possible in principle to measure each duct after each energization of the actuator. In this way, any irregularity which may have a negative effect on the print quality can be traced “on-the-fly” very accurately so that adequate action can be taken to obviate such a negative effect.
However, the known method has one significant disadvantage. Particularly when used in a printer with a large number of ink chambers, for example 100 or more ink chambers per printhead, the “on-the-fly” measurement of all the ink chambers results in a very high data rate of the signals for analysis. To enable these signals to be processed directly requires complex and hence expensive electronics.